Figure 11.
J104915.57 - 531906 in the WISE
data. He then recovered the object in other earlier surveys to
obtain a more accurate distance
measurement.
The outstanding question remained: “What is this object?”
Director’s Discretionary Time
enabled spectroscopy with the
Gemini Multi-Object Spectrograph (GMOS) on Gemini South
to provide an answer, and more.
Luhman classified the object
as an L8 dwarf, showing good
agreement with a template
spectrum. For ages less than 10
billion years, the temperature
is well below that of the hydrogen burning
limit. Also, considering the strong lithium
absorption, Luhman concludes that the object is a brown dwarf.
As an unexpected bonus, the acquisition
image resolved the source into two components (Figure 11). The pair, separated by 1.5
arcseconds, corresponds to 3 astronomical
units at the object’s determined distance.
Examination of earlier, archival images does
not show either source at their present location, arguing that they form a common binary system.
The secondary is only about half a magnitude fainter than the primary, which suggests that it is also a brown dwarf and near
the L/T spectral class transition. Brown dwarf
models are sensitive to age, so a binary system offers robust tests of models and potentially strong constraints on mass, assuming
the objects formed at the same time.
The GMOS observations were obtained on
February 23, 2013, and the full paper is published in The Astrophysical Journal, available
at: http://arxiv.org/abs/1303.2401,
as is more information from
http://www.gemini.edu/node/11966.
WISE J104915.57 - 531906
appears as a single
object at the center of the
larger image from WISE.
The inset shows higherresolution observations
using GMOS-South,
which revealed its
binary nature (inset) and
enabled classification of
the brown dwarf pair.
Light Echoes Show the Asymmetric
Explosion of SN1987A
Observations of light echoes — reflections
of a transient event in the surrounding material — allow astronomers to change perspective. Rather than being effectively fixed
to a viewpoint on Earth, light echoes reveal
the source object from a variety of viewing
angles. Brendan Sinnott (McMaster University) and colleagues used light echoes from
supernova 1987A (SN1987A) to conclude
that this Type II event was asymmetric, with
an elongated 56Ni structure. The strongest
asymmetry they measure is in the Ha line,
and this asymmetry aligns well with the observed axis of ejecta.
The five fields the team observed with GMOS
on Gemini South probe the supernova emission over its first 300 days. Figure 12 shows
the prominent light echos, which appear as
nearly circular rings, along with the slit positions on the GMOS fields.
Variations in spectra obtained at different locations alone do not imply asymmetry in the
supernova emission. The source spectrum itself changes, so the reflected light depends
not only on the dust properties and its dis-
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